fix templating

Author: mallport

.nais/alerts.yaml

@@ -23,7 +23,7 @@ spec:
             severity: critical
             alertmanager_custom_config: dapla-stat
             alert_type: custom
-            cluster: { { cluster } }
+            cluster: {{cluster}}
 
         # This alert detects high CPU usage by calculating the CPU time used over 5 minutes.
         - alert: HighCPUUsage